Hydraulic actuator and sensing mechanism



Nov. 15, 1966 R. B. ANNAT ETAL 3,235,140

HYDRAULIC ACTUATOR AND SENSING MECHANISM Filed Aug. 20, 1964 I n entor P055477 BUCHAAM/VUA/VA/ZT & JOH/V sum/15y PfD/P/CK A ttorrzeys have an effect on the other.

United States Patent 3,285,140 HYDRAULIC ACTUATOR AND SENSING MECHANISM Robert Buchanan Annat, Kenilworth, and John Stanley Pedrick, Coventry, England, assignors to Massey- Ferguson Services N.V., Curacao, Netherlands Antilles Filed Aug. 20, 1964, Ser. No. 390,924 Claims priority, application Great Britain, Aug. 27, 1963, 33,799/ 63 3 Claims. (Cl. 91-217) This invention relates to tractors of the type having an hydraulic power lift including a hitch linkage having a pair of sidewise spaced draft links by which an implement of trailer can be hitched to the tractor; and hydraulic ram mechanically connected to said linkage for raising and lowering it; a pump which supplies hydraulic liquid to the ram; and a control valve to control the supply of the hydraulic liquid.

In the United States patents issued to E. V. Bunting, Nos. 2,627,796 and 2,627,815 there are shown hydraulic systems suitable for use on a tractor having a hydraulic lift ram which system provides a constant predetermined pressure in the lift ram that can be varied by manipulation of a control lever. The systems shown in these patents are directed to what is commonly called suction side pump contro wherein volume and pressure supplied by the pump is controlled by opening and closing the inlet to the pump which is constantly connected to the lift ram while simultaneously closing and opening the ram to the oil sump.

The systems described in the Bunting patents cannot be used where oil under pressure is required for other elements than the lift cylinder since any changes in demand either by the lift control or by the other elements would The arrangements shown in the Bunting patents referred to above utilize a floating lever follow up construction for operating the control valve. The floating lever construction requires a relatively fine adjustment and usually a considerable space is required for the control.

It is, therefore, an object of this invention to provide a simple control system for maintaining a predetermined constant pressure in the lift cylinder of a tractor or other vehicle.

It is a further object to provide such a control system wherein the cylinder pressure can be controlled independently of the flow of fluid through the pump.

Still another object of the invention is to provide a pressure control system for operating a hydraulic lift cylinder which utilizes a simple reciprocating follow up system.

A further object is to provide a pressure control system for operating a hydraulic lift wherein the desired degree of pressure can be instantly set with a gradual build up of pressure to the desired level.

In carrying out the foregoing, and other objects, a lift system is provided having a hydraulic ram to which hydraulic fluid is supplied from a reservoir by a pump. Interposed between the pump outlet and the ram is a control valve which is movable between first, second and third positions in which the hydraulic fluid in the ram is drained from, trapped or increased, respectively. The control valve is actuated between positions by a piston and cylinder in pressure communication with the ram. Either the piston or cylinder is normally fixed relative to the valve such that variations in pressure Within the cylinder causes the non-fixed member of the piston and cylinder to move relative to the control valve. The non-fixed, or movable member in turn is connected with the control valve to actuate the control valve in accordance with pressure changes in the ram as sensed by the piston and cylinder.

The piston and cylinder are interconnected by a spring which acts against the pressure within the cylinder, and the force of the spring determines the constant pressure that is to be maintained at the ram. Accordingly, the position of the fixed member of the piston and cylinder is made selectively adjustable so as to vary the force of the spring and thus the pressure to be maintained at the ram.

Other objects, advantages, and features of the invention will become apparent from the following description taken in connection with the accompanying drawing in which the single figure diagrammatically illustrates a hydraulic lift system according to the present invention.

While the invention will be described in connection with a specific embodiment, it will be understood that it is not intended that the invention be limited to the specific construction and arrangement shown. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope and spirit of the invention as defined by the appended claims.

Referring now to the drawing, a continuously driven pump 11 delivers liquid from the reservoir 12 through a conduit 13 to the control valve, indicated generally at 14. The control valve is bolted to the housing 9 of a tractor. An example of tractors having lift systems with which the present invention may be employed is disclosed in the copending US. patent application of Bunting et al., Serial No. 359,076, filed April 13, 1964, the disclosure of which is incorporated herein by reference.

The control valve 14 operates to pass liquid from the pump 11 to the main ram cylinder 15 to displace the main ram 16, in this case the control valve can be said to be in the third or raise position; alternatively the control valve 14 can operate to block the return of liquid from the ram cylinder 15, while at the same time returning liquid from the pump 11 to the reservoir 12, this position being the second or neutral position; finally the control valve can allow the liquid from the ram cylinder 15 to spill to the reservoir 12 while at the same time returning the liquid from the pump 11 to the reservoir, this being the first or 'lower position. Piston 16 is connected to a rocker arm A for operating lift arms B, which, through drop links C raise and lower draft links D pivotally mounted on the rear of the tractor.

Control valve 14 includes a generally cylindrical plunger 17 slidable in a bore in the stationary valve body and provided with an annular part 18 of reduced diameter.

Plunger 17 is illustrated in the second or neutral position in which a full diameter portion or land 19 of the plunger 17 blocks off a conduit 20 leading to the main ram cylinder 15, thus preventing liquid from spilling therefrom. The grooved part 18 at the same time places the conduit 13 in communication with a conduit 21 which returns liquid from the pump 11 to the reservoir 12.

If plunger 17 is moved to the left until portion 19 abuts a stop 22, the valve is then in the first or lower position, as the part 18 allows liquid to spill from the ram cylinder 15 through the conduits 20 and 21, and simi larly recirculates pumped liquid to the conduit 21 and reservoir 12.

If plunger 17 is moved to the right to the limit of its travel determined by a cover plate 43, the valve is then in the third or raise position, as the portion 19 will block off conduit 21 and the part 18 will cause liquid to be delivered from the pump 11 through a check valve 10 to the conduit 20 and ram cylinder 15.

Mounted on the tractor housing 9 is a bracket 41 which provides a support for a pair of rails 42 from which there is slidably suspended apressure sensing and control assembly. This assembly includes a hydraulic cylinder 24 and piston 25 connected through a conduit 37 to the ram cylinder 15. Piston 25 is connected with control valve plunger 17 by means of a rod 26, shoulder 27 and links 28 and 29. An outer cylinder 30 surrounds the cylinder 24 and is aifixed thereto, and extends over the shoulder 27 and part of the link 28, the end portion opposite cylinder 24 defining a spring seat. Interposed between cylinder 30 and the abutment is a compression spring 38 urging the piston 25 to the right hand side (as viewed on the figure) of cylinder 24 against fluid pressure within cylinder 24.

7 Two brackets 35 are provided on the underside of cylinder 30 and a compression spring 36 is carried between brackets 35 which bears against thrust collars 39 fixed to a rod 34. Rod 34 is in turn connected through a link 33 to a control selector handle 31 mounted on a bracket 32 bolted to the tractor housing 9.

With the arrangement described, pressure will occur in the main ram cylinder 15, due to the supply of liquid from the pump 11, and/or to external conditions affecting the draft links, for example the weight of an implement, or changes in the forces on an implement being towed behind the tractor. This pressure in the cylinder will, through conduit 37 and piston 25, tend to compress spring 38.

In operation, let it be assumed that control valve plunger 17 is in the neutral position (as illustrated) and that there is a certain predetermined pressure in the ram cylinder 15. If due to external conditions, such as a change in the forces acting on the ram, piston 16 moves so as to cause a fall in this pressure, there will be a corresponding decrease of pressure in cylinder 24 allowing spring 38 to move the links 28 and 29 and control valve plunger 17 to the right, that is into the third or raise position. As a result, liquid will now be supplied from pump 11 to the main ram cylinder 15 until the predetermined pressure is reached once again. Conversely should the pressure in the cylinder 15 rise above the predetermined value, the corresponding rise in pressure in cylinder 24 will cause the spring 38 to be further compressed and the plunger 17 to be moved to the left into the first or lower position, in which case liquid will drain from the ram cylinder 15 and decrease the pressure to its predetermined value at which the pressure in cylinder 24 will balance the force of the spring 38 and the plunger 17 will be in the neutral position.

Variation of the predetermined value at which the pressure in the ram cylinder is maintain d is eifected by adjustment of the selector 31 to vary the spring pressure on the shoulder 27. Assuming the ram 16 is connected to the draft links in such a way that movement of ram leftwards would raise the draft links, then movement of the selector 31 in an anti-clockwise direction would raise the predetermined pressure in the system, and raise the draft links; movement of the selector 31 in a clockwise direction would lower the pressure in the system.

As movement of the valve plunger 17 is limited compared with the range of movement of the rod 34 the brackets 35, collars 39 and spring 36 act as a break-out device to allow the selector 31 to be fully moved to its required position without the necessity of having to follow the cylinder 30 as it moves due to changes in the pressure. If the break-out device were not provided it would only be possible to move the selector handle slowly to follow the pressure rise, or pressure fall, depending on which direction it was being moved. If the selector is being moved anti-clockwise to give a pressure rise, that is in the raise direction, then it may be moved to the .full extent of its desired position immediately; in consequence the plunger 17 will be moved to the right as" far 'as it will go into the raise position. The breakout device will cause the spring 36 to compress and move away from the left bracket 35; as the pressure in the cylinders 15 and 24 rises the whole assembly 23 will gradually move to the right until such time as the force on 4 the piston 25 exerted by pressure in the cylinder 24 balances the force exerted by the spring 38.

The selector 31 has, as stated above, two functions; it can be used to set a certain predetermined pressure in the hydraulic system and it can be used to raise and lower the draft links (and an implement attached to them) between the transport and working position respectively. If the selector is moved anti-clockwise to the raise position, the pressure exerted by the spring 38 is such that the hydraulic pressure required in cylinder 24 to return the plunger 17 to the neutral position is high enough to raise the draft links to the transport position; at this position the plunger 17 will be in the neutral position, thus blocking the conduit 20 and holding the draft links in the transport position; it is preferable that a latch be provided to hold the draft links in the transport position, in order that the selector 31 may be moved clockwise to relieve the oil pressure.

Although the invention has been described with relation to one particular type of tractor power lift hydraulic system, it may be applied to many other existing types.

One advantage of this particular embodiment of the invention is that the pressure of the spring 38 does not require to be overcome manually due to the fact that within limits its pressure is continually balanced by the pressure in the cylinder 24. As a result of this the sliding friction required on the rails 42 and selector linkage 31 and 33 to resist the resultant end thrust are very much reduced. If the pressure was not balanced, the force necessary to compress the spring 38 manually with the selector 31 in the raise position would require a fairly high friction-a1 hold in the selector linkage.

Having described a specific embodiment of the invention, what is claimed is:

1. In a tractor having draft links pivotally anchored to the tractor body, a hydraulic ram mechanically connected to raise and lower the draft links, a fluid source for supplying hydraulic medium to the ram, and a control valve for connecting and disconnecting the ram with the source and exhaust, pressure sensing means in the form of a piston displaceable in a cylinder in accordance with variations in hydraulic pressure, the cylinder being hydraulically connected to the ram to sense the hydraulic pressure therein, an operative connection between the piston .and the control valve whereby movement of the piston as a result of a pressure change imparts movement to the control valve in a manner tending to return the ram pressure to a predetermined Value, means resiliently interconnecting said piston and said cylinder, selector means adapted selectively to vary the predetermined valueat which the hydraulic pressure in the ram is maintained, and said piston being displaceable in either of two directions to move the control valve through said operative connection, and said cylinder being adapted to be positioned at varied positions in either of said two directions under the influence of the selector to vary said predetermined pressure.

2. The construction claimed in claim 1 including a resilient interconnection between said selector means and said cylinder, acting as a break-out device.

3. A lift system for a vehicle comprising a hydraulic ram extensible and retractable in response to increases and decreases respectively in hydraulic pressure, a fluid source for supplying hydraulic fluid to the ram, a control valve between the source and the ram movable between a first position to exhaust fluid from the ram to decrease the ram pressure, a second position to trap fluid in the ram to maintain the existing ram pressure, and a third position to connect the ram with the source to increase the ram pressure, a cylinder hydraulically connected to the ram, a piston reciprocable in the cylinder to sense the ram pressure and having a rod operatively connected to the control valve for actuating the valve to increase or decrease the ram pressure in response to decreases and increases, respectively, in the pressure in said cylinder,

means carried by the cylinder defining a spring seat, an abutment on the piston rod, a spring seated between the spring seat and abutment for exerting a biasing force on the piston independently of the ram pressure and means for adjusting the position of the cylinder relative to the piston to vary the biasing force of the spring to adjust pressure to be maintained at the ram, a selector lever for adjusting the position of the cylinder, a resilient connection between the selective lever and the cylinder providing a break-out connection, and said selectively adjusting means including a pair of rails extending parallel to the direction of reciprocation of the piston, said cylinder being slidably mounted on said rails, a rod slidably mounted on said cylinder, spring means connecting the rod with the cylinder, vand a selector lever operable to actuate the rod relative to the cylinder to compress the spring and urge the cylinder to move relative to the piston and control valve.

References Cited by the Examiner UNITED STATES PATENTS 2,312,464 3/1943 Ziebolz 91-433 2,439,325 4/1948 Wiesendanger 91433 2,878,785 3/1959 Rexford 91433 3,101,977 8/1963 Hyler et al. 91433 FOREIGN PATENTS 691,449 5/ 1940 Germany.

MARTIN P. SCHWADRON, Primary Examiner.

PAUL E. MASLOUSKY, Examiner. 

1. IN A TRACTOR HAVING DRAFT LINKS PIVOTALLY ANCHORED TO THE TRACTOR BODY, A HYDRAULIC RAM MECHANICALLY CONNECTED TO RAISE AND LOWER THE DRAFT LINKS, A FLUID SOURCE FOR SUPPLYING HYDRAULIC MEDIUM TO THE RAM, AND A CONTROL VALVE FOR CONNECTING AND DISCONNECTING THE RAM WITH THE SOURCE AND EXHAUST, PRESSURE SENSING MEANS IN THE FORM OF A PISTON DISPLACEABLE IN A CYLINDER IN ACCORDANCE WITH VARIATIONS IN HYDRAULIC PRESSURE, THE CYLINDER BEING HYDRAULICALLY CONNECTED TO THE RAM TO SENSE THE HYDRAULIC PRESSURE THEREIN, AN OPERATIVE CONNECTION BETWEEN THE PISTON AND THE CONTROL VALVE WHEREBY MOVEMENT OF THE PISTON AS A RESULT OF A PRESSURE CHANGE IMPARTS MOVEMENT TO THE CONTROL VALVE IN A MANNER TENDING TO RETURN THE RAM PRESSURE TO A PREDETERMINED VALUE, MEANS RESILIENTLY INTERCONNECTING SAID PISTON AND SAID CYLINDER, SELECTOR MEANS ADAPTED SELECTIVELY TO VARY THE PREDETERMINED VALUE AT WHICH THE HYDRAULIC PRESSURE IN THE RAM IS MAINTAINED, AND SAID PISTON BEING DISPLACEABLE IN EITHER OF TWO DIRECTIONS TO MOVE THE CONTROL VALVE THROUGH SAID OPERATIVE CONNECTION, AND SAID CYLINDER BEING ADAPTED TO BE POSITIONED AT VARIED POSITION IN EITHER OF SAID TWO DIRECTIONS UNDER THE INFLUENCE OF THE SELECTOR TO VARY SAID PREDETERMINED PRESSURE. 